Magnetically acting speedometer



Patented Aug. 4, 1953 MAGNETICALLY ACTING SPEEDOMETER Charles Hilaire Henri Rodanet, Neuilly-sur-Seine, France, assignor to Etablissements Ed. Jaeger,

Seine, France Application May 31, 1950, Serial No. 165,230 In France November 15, 1949 2 Claims. 1

The present invention relates to improvements in magnetically-acting speedometers of the type in which a permanent plane magnet with concentrated induction field, rotating about an axis at right angles to its plane and consisting of a magnetic material agglomerated under high pressure, drives a movable unit comprising a suspended member of non-magnetic material having a low moment of inertia, this speedometer being thermo-magnetically compensated by means of a self-compensating shunt made of a metal having a very low Curie point and mounted on the magnet. This self-compensating shunt may be mounted on the plane magnet like a binding or hoop member and encloses the lateral surface of this plane magnet.

In some applications such as, for instance, the use of a speedometer of this type in aviation, the self-compensating shunt made of metal having a very low Curie point willnot ensure the desired thermo-magnetic compensation in the whole range of temperature variations to which the apparatus may be subjected.

In order to avoid this drawback and render it possible to use such speedometers within temperature ranges of the order of for example 50 F. and 149 F., the present invention has for its main object to provide a magnetically-acting speedometer of the kind described, wherein the thermo-magnetic self-compensating effect is obtained by means of a pair of shunts made of different metals having different expansion and magnetization coeflicients, one shunt serving for cold operation and the other for warm operation.

According to a preferred embodiment of the invention, these shunts are mounted on the plane magnet of agglomerated magnetic material in the way of binding or hoop members obtained, preferably, from metal strips cut and shaped according to the outer contour of the plane magnet and having their adjacent ends connected together in any suitable and known manner such as electric welding, clamping, etc. The shunts are preferably made of thermostatic metals or alloys having different percentages of silicon therein.

The ensuing description made in reference to the accompanying drawings, given by way of non-restrictive examples, will provide a clear understanding of the way in which the invention may be put into practice.

Fig. 1 is a view in elevation and partly in section of a speedometer according to the invention.

Fig. 2 is a side view partly in section of Fig. 1.

Fig. 3 is a plane view partly in section of Fig. 1.

The flexible drive cable extending from the member the speed of which is to be measured is made rigid with the drive spindle I of the speedometer through any known means not shown, such as a square drive socket for instance. Said spindle I is centered in a bearing 2 integral with the general support 3 of the apparatus. On said spindle there is mounted in a manner known per se, a pinion 4 adapted to drive the totalizing device which may be of any general type.

Said spindle supports at its top end a ring 5 on which is rigidly mounted a flat magnet 6 having six poles on its face I. Said magnet is constituted by any agglomerated material such as iron powder, aluminum-steel powder, etc.

In alignment with the axial line of the drive shaft I, a spindle 8, the movable structure spindle, is mounted on two bearings 9 and It. The bearing 9 rigid with the strip II secured to the frame 3 comprises a cup member I2 through which extends the spindle 8, a washer I3 and a stop ring I4 press-fitted around the spindle and leaving a longitudinal clearance between the internal face of the cup 12 and the Washer I3 applied against the bearing-surface I5 of the spindle 8. The cup I2 is made rigid with the strip II by crimping. The second bearing III of the spindle 8 is formed by a bore made in a cage Il rigidly connected with the strip I I through posts I8, the assembly as a whole constituting a cage.

In overhanging relation with respect to the bearings 9 and I0, the spindle 8 supports a disc I9 of a non-magnetic metal, aluminum for instance, the external diameter of which is substantially greater than that of the flat magnet 6. Said disc I9 is mounted on the spindle 8 through the medium of a shouldered ring 20 and a washer 2I press-fitted over said ring.

The field-closing plate 22, made of soft steel or silicon-containing sheet iron for instance. is provided with a port 23 allowing it to be mounted above the movable disc I9. It moreover traverses two slots 24 formed in the body of the frame 3 and is secured to bosses carried by the latter by means of bolts 25 respectively extending through a bore 26 formed in the end of the plate 22 opposite from the port 23 and the restricted portion 21 of said port. Between the plate 22 and the bosses 28 springs rounding the bolts 25. The bolts 25 serve to adjust the position of the field-closing plate 22 with respect to the fiat magnet 6 and conse quently the total air-gap, thus allowing the determination of the various ranges for the maxi- 29 are inserted tightly surboth in cold and warm conditions, the magnet is thermomagnetically compensated by a pair of bers made of difierent metals like those used in altimeters, these metals having difierentexpan sion and magnetization coetfici'entsz"'l"he binding or hoop members 3i and 32 have different widths and the former acts as .cold operationt shunt while the latter acts as warm operation shunt.

According to a preferred form of embodiment, the binding member 3! consists of a metal having a Curie point of 50 F; and a magnetic'vanishing range comprised between-40 F. and 50 R; such as the alloy used in altimeter's and which comprises:

Percent Carbon .11 Magnesium 1.12 Silicon .13 Nickel 29114 The binding member 32 consists of a metal having a Curie point of 149 F. and a magnetic vanishing range comprised between 68 and 149 R, such as the alloy used in altimeters and which comprises:

Percent Carbon .08 Magnesium 1 .02 Silicon .01 Nickel 30.

The spiral spring cm which supplies the antagonistic action against the drive of the movable disc !9 by the flat rotating magnet 5 has one of its ends secured to a ring32a;rigidly,

mounted on the spindle 8. Its other end is se cured to a hook 33 forming part of the'part I6;

The latter is mounted with a. sOft friction fit onthe external portion of the cage 12. As a result the zero-adjustment of the speedometer may be eifected in an approximate manner on mounting, but is finally accomplished in the initial operations of the speedometer through theretarded.

rotation of the attachment of the spiral spring lfi'about the cage [2.

The simplicity in vmounting the constituent elements of the speedometer according to theinvention, as well asthe compact form of their 4 assembly, makes it possible to realize the fram 3 in the form of a unitary frame.

It will be quite evident that without exceeding the scope of the invention, modifications may be made in the forms of embodiment of the various elements constituting the speedometer, especially as regards the-shape of the low-inertia member, the shape of the field-closing plate, the number of poles of the flat magnet, the construction of the adjustable bearing for the movable structure spindle etc. r Whati claim is:

1. In combination with a magnetically-acting speedometer of the type in which a permanent plane magnet having a cylindrical contour and a concentrated induction field, rotating about an axis perpendicular to its plane and consisting of a magnetic material agglomerated under high pressure, drives a movable unit comprising a member made of non-magnetic metal suspended and having a low moment of inertia, of a first ring acting as the hoopmember-and' made of .a metal having a relatively low Curie point and a magnetism vanishing range, said first hoop member being mounted peripherally, on said plane magnet in the portion thereofwhich is nearest to,

th member of non-magnetic metal, and of-a second ring acting also as a hoopmember and made of a metal havingia Curie point substantially higher than the metal of, the first hoop member and a magnetism vanishing range the extreme temperatures of which are higher than those of the correspondinglrange of said first hoop member, said second hoop member being mounted peripherally on the contour of said plane magnet opposite to said first hoopmember with respect to the member of non-magnetic metal.

2. A combination, according to claim 1 wherein the metals of the first'and second hoop members are made have Curie points of 50 F. and 149 F., and magnetism vanishing, ranges com prised between 40 F. and 5071". and between 68 and 149 respectively;

CHARLES HILAIRE I -IENRI RODANETQ References Cited in the fileof this patent UNITED STATES PATENTS Number Name Date 1,697,148 Spoon'er Jan. 1,1929 1,597,580 Wallis Jan. 1, 1929 1,968,971 Sullivan 1. Aug. '7, 1934 1,988,568 Randolph Jan. 22, 1935 2,159,389 Le Fevre. May 23,1939 2,232,789 Kollsman Feb. 25,1941; 2,372,633 Angold Mar. 27, 1945 

